1. Field of the Invention
The present invention relates to an abnormality detecting device of an electric power converting device and an abnormality detecting method, and particularly to an abnormality detecting device for detecting a short circuit fault in a switching element forming an electric power converting device as well as an abnormality detecting method.
2. Description of the Background Art
In recent years, hybrid vehicles and electric vehicles have received attention as vehicles developed in view of environments. The hybrid vehicle uses, as a drive power source, a DC power supply, an inverter and an electric motor driven by the inverter in addition to a conventional engine. More specifically, the engine is driven to provide the drive power source, and further the inverter converts a DC voltage provided from the DC power supply into an AC voltage for driving the motor by the converted AC voltage to provide the drive power source.
The electric vehicle uses, as a drive power source, a DC power supply and an inverter as well as an electric motor driven by the inverter.
In the motor drive device mounted on the hybrid vehicle or the electric vehicle, when an abnormality such as a short fault in a switching element forming the inverter is detected, the inverter usually stops its operation to prevent overheating of the switching element due to passage of an excessive current through the short-circuited switching element.
For example, Japanese Patent Laying-Open No. 08-308244 has disclosed an abnormality determining method relating to an electric power converting device having a power converting unit in which three sets of switching arms each formed of two switching elements connected in series together are arranged in parallel between DC power supplies, and the switching operations of the switching elements convert the DC power into a three-phase AC power. In this electric power converting device, the above method successively turns on the six switching elements of the electric power converting unit according to a plurality of predetermined combination patterns, and determines the shorted faulty switching element based on changes appearing in an output or input current of the electric power converting unit.
In the above method, when the six switching elements are successively turned on, an output current detector detects a current only when two pairs of arms other than the arm including the faulty or defective switching element are in such a state that the switching elements of these arms located in the vertically opposite positions, respectively, are turned on. Based on this fact, a pattern required for determining any short fault in the switching elements as well as a logical table used for the determination are set or determined.
Japanese Patent Laying-Open No. 07-071805 has disclosed a control device of an air conditioner that includes arbitrary element turn-on means for turning on an arbitrary one of switching elements of an inverter unit, overcurrent detecting means for detecting an overcurrent flowing into the inverter unit, and self-diagnosis means for checking a short circuit of the switching elements by detecting the overcurrent flowing into the inverter unit.
According to this device, when an arbitrary element is turned on and a switching element connected in series to this arbitrary element is short-circuited, a short circuit current flows through a path extending from this arbitrary element to the switching element in question. An overcurrent detection circuit receives a detection value of a current detector connected between the switching element and a smoothing capacitor, and provides an overcurrent detection signal to a microcomputer. The microcomputer receives the overcurrent detection signal, and determines that the switching element in question has a short fault.
Further, Japanese Patent Laying-Open No. 2005-210830 has disclosed an abnormality detecting method for an inverter that includes a plurality of interconnections supplying a drive voltage of multiple phases to a motor, a plurality of positive arm elements supplying a positive drive voltage to the plurality of interconnections, respectively, and a plurality of negative arm elements supplying a negative drive voltage to the plurality of interconnections, respectively. This method includes the steps of successively switching the plurality of negative arm elements, successively switching the plurality of positive arm elements after the above step, determining a conduction state of the plurality of interconnections or a bus line by an arithmetic processing device based on a current signal or a bus current signal in response to every switching of one of the plurality of the negative and positive arm elements, and providing a first error signal by determining a “short fault” of one of the plurality of elements by the arithmetic processing device when a current flows through any one of the plurality of interconnections or the bus line.
Each of the abnormality detecting methods disclosed in the foregoing Japanese Patent Laying-Open Nos. 08-308244, 07-071805 and 2005-210830 determines the shorted faulty switching element based on changes that appear in current flowing through the inverter when the arbitrary switching element is turned on.
In this configuration, however, the overcurrent is detected when the arbitrary switching element (e.g., an upper arm of a U-phase arm) is turned on in either of the case in which the switching element (a lower arm of the U-phase arm) connected in series to the above switching element is shorted and the case in which short circuit occurs in a switching element (e.g., a lower arm of V- or W-phase) that belongs to the arm other than the U-phase arm and is vertically opposite to the above turned-on switching element. Therefore, it is impossible to accurately determine the shorted faulty switching element from a result of the detection of the overcurrent.